The arrangement of histones in nucleosomes is still not known. Ifistone HI has a. short ammo end piece, a globular core, and an extended carboxy tail end. One model is that the globular part binds to the entry/exit portion of DNA on the nucleosome and the carboxy tail binds the linker DNA. A variant of H I is being used to test this model. It is GH5, from avian erythrocytes, with a cysteine genetically engineered near the carboxy terminus, which can then be Au-labeled. So far, it has been labeled and the nucleosome/DNA complex studies with GH5 are underway.